The Observant Astronomer

The passing scene as observed by an observant Jew, who daylights as an astronomer.

Thursday, August 24, 2006

Defining "Planet" III

After having ten days to think about, and discuss the issue, the International Astronomical Union General Assembly has declared itself on the definition of planet. (You can read the on-line part of the discussion in this electronic supplement to the GA newspaper.)

Their discussions have led to a revised set of definitions. These are in two resolutions, each with a possible amendment.

Resolution 5 (Resolutions 1-4 relate to coordinate systems in space and time and IAU housekeeping) is the planet definition resolution. It divides the solar system into three groups: Planets, dwarf planets, and Small Solar System Bodies, as follows:
(1) A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
What's new here is clause (c). The idea here is that a planet dominates the mass distribution in its immediate vicinity. There can be a small amount of stuff left (e.g. the Trojan asteroids associated with Jupiter), but any number of similarly-sized objects in similar orbits violates this clause. Thus both Ceres and Pluto are excluded. Historically, this is how Ceres was demoted the first time, and now Pluto has joined it in the next category. The end result is that there are eight currently known planets. (The amendment would have added "classical" to this definition, leaving the word "planet" on its own still undefined, but this was defeated.)

(2) A dwarf planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
The new clauses here are (c) and (d). Clause (c) distinquishes the dwarf planets, while (d) excludes Charon in particular. There are no double planets under this definition.

(3) All other objects except satellites orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".
This term replaces "minor planet" now that the dwarf planets have been segregated out. This term is very unwieldy and I suspect something else will come into general use. Half the time I get the "S"s mixed up and say "Solar System Small Bodies".

Resolution 6 defines a new class of object dwarf planet with Pluto as the prototype. Up until now we've been calling them they've been included under the rubric of "Kuiper Belt objects", but the failed amendment would have changed this to called them "plutonian objects".

Left undecided was what we should call the current asteroid belt, now that it is made up of a combination of dwarf planets and small bodies. Shall these be '"ceresian objects" travelling in the "ceresian object belt"?

UPDATE: except satellites in paragraph 3 was a late amendment according to my source in Prague who has also clarified the purpose of Resolution 6. The amendment was very narrowly defeated, and an "IUA process" will be established to come up with a better name.

Tisha b'Av

(I know Tisha b'Av was three weeks ago, but I figure better to post this now than to leave it on the drive for a year.)

If Tisha b'Av is the most difficult fast, it isn't because of its length, or even because it starts and ends late (at extreme northern latitudes anyway). No, it is difficult because it is the most boring of all the fast days. Yom Kippur is longer, but you are kept so busy, and, one hopes, spiritually heightened, with all the goings on that there often isn't time to think about your empty stomach. But on Tisha b'Av? I know someone who spends most of The Nine Days trying to figure out what she can do on the day itself. Perhaps "This", or "That" useful, productive occupation. My response is that you're not permitted to do This or That because you are supposed to sit on the floor and cry because the Beis Hamikdash is in ruins. For most of us, though, that's a pretty difficult level to reach.

One year, I went to the Kotel on Tisha b'Av. After maariv and Eicha, a neighbour invited us to go up to up to Yerushalayim with his family, so we all piled into their station wagon and went. We had to park some distance away, but then we walked into the Old City to get as close as we could to that focal ruin. It must have been around one in the morning at this point. The crowds had gone home, but some people still lingered. I expected strong displays of emotion, crying and weeping. Visible sadness, at the very least. Instead it was almost a festive atmosphere. Some sat on the stone paving of the plaza and chatted. Others were still saying kinos. There was a sense of waiting for something, but no one was quite sure what. Standing at the Kotel, looking up at the place where the Temple ought to stand, I tried to feel something, but couldn't.

This year I was in a shtible in the provinces (i.e. outside London) on Tisha b'Av. In most places I've been, everyone just says the daytime kinos at his own pace, but there everyone takes turns leading a few kinos. I wasn't the only visitor. There was another fellow, and for whatever reason, he couldn't figure out the proposal when it was first explained. So he took his place on the other side of the room and started saying kinos by himself, while the rest of us started up the first round. And before long, we heard sobbing. Sobbing that went on for the better part of the several hours. Here was a person who was actually feeling something on Tisha b'Av! Now I am the sort of person who keeps his emotions under tight control, but I tried a little experiment after an hour or so of crying behind me. While continuing to say the current kina, I opened the gate I keep closed upon grief and allowed it out. I didn't quite cry, but the grief welled up for a while until I bottled it back up before it could overwhelm me. I think I'll let it out again next year though, if we're still here in exile. If we can stimulate simcha on Simchas Torah, surely a bit of stimulated mourning is also in order.

Friday, August 18, 2006


A number of times while in the UK I passed by a building of the established faith which had the following sign out front:
This life is meant for caring.
And the next life, it's meant for casual indifference?

Defining "Planet" II

Further to my previous post, here is an interesting article from the US Naval Observatory discussing the time when (1) Ceres was last a planet, and how it lost that status.

And this is a new technical paper (in PDF format) by Steven Soter at AMNH that discusses an alternative physically-motivated definition of planet. (The middle bit is somewhat technical, but Section 1 gives a good historical summary, and the rest can be skimmed with profit.) This is an eight-planet solution.

After a couple of day's reflection, I think that, if the proposed definition passes, and especially if the number of planets under this definition becomes unreasonable (e.g. 53 planets as claimed by Brown), then the end result will be the same as Soter's. As written, the proposal creates a primary distinction: classical planets (Mercury through Neptune) vs. plutons ( Pluto, Charon, 2003 UB313, and probably more). All of the latter are also included in the category of dwarf planets, in addition to Ceres, and possibly 3 other asteroids. Now, when the number of plutons becomes excessive, and the category of dwarf planets overloaded, it will be convenient to forget that plutons are planets and both "pluton" and "dwarf planet" will take on the connotations now attached to the soon-to-be-discarded "minor planet". The upshot will be a sensible eight-planet solar system, but with time to soften the emotional blow a sudden, full-scale demotion of Pluto would entail.

Wednesday, August 16, 2006

Defining "Planet"

The 26th Triennial General Assembly of the International Astronomical Union has opened in Prague, and the first press release deals with the proposed definition of the word planet. The Globe and Mail has a reasonably good popular level article. (CNN's is appallingly bad and manages to not only suggest that this is the only reason for having a GA, but also confuses the solar system with the galaxy. Of this sentence:
Far outside the realm of science, astrologers accustomed to making predictions based on the classic nine might have to tweak their formulas.
there is little that can be said.)

In short, the proposal is that planets are objects which orbit a star and are in hydrostatic equilibrium. (I.e. that the gravitational force inwards is balanced by pressure outwards. "Small Solar System Bodies", the excluded category, are supported by chemical and mechanical forces, i.e. the strength of their constituent rocks.)

The novelty is the distinction between the eight classical planets---Mercury through Neptune---and a new class called "plutons", which are planets in highly eccentric or inclined orbits. The prototype is Pluto, which, with its moon Charon, are to be considered a double planet. Newly discovered 2003 UB313 would also be a pluton, with possibly many more waiting in the wings. The currently minor planet (a term to be deleted from the lexicon under the proposal) (1) Ceres would regain its planetary status. All of these would be called "dwarf planets". There are potentially another dozen dwarf planets (all but three plutons) waiting in the wings.

There will be several session to discuss the issue over the next two weeks, with a vote likely on 24 August.

Tuesday, August 15, 2006

Light Travelling

What with the new travel restrictions, Shabbos we got into a discussion of the practicalities of travelling without cabin baggage, especially on long flights. At that point it wasn't clear that the no-baggage requirement only held on the UK to US flights. So what, we wondered, would a person do if he were flying to, say, Australia? It's a 20-hour flight from the UK, you'll have to daven shacharis at least once, usually twice, along the way, not to mention mincha and maariv. So you'd better have the siddur memorized, because you can't take it on the plane. That's possible, but memorization isn't going to help you with tefillin. Skipping the mitzvah would be a victory to the Islamists, so what to do?

Option 1: Somebody, Chabad say, puts a carefully tested pair of tefillin on every plane. Just in case. Be generous, Rashi and Rabbenu Tam. Also a set of straps for lefties. Some siddurim too, of various nusachs.

Option 2: On Shabbos you could wear tefillin in the street because they are a garment. So the solution is to wear your tefillin onto the plane. We should resurrect the custom of wearing them constantly. Tallis too. Then they become recognized religious garb and we can't be prevented from bringing them wherever we want to.

Books are also banned, unless they're purchased on the other side of security. So we need to get all the airport bookshops to sell small siddurim, tehillim etc. along with all the newspapers and other travel necessities.

Option 3: The authorities finally get their act together and recognize who the real threat is. Just a clue: It isn't observant Jews, certainly not those travelling with a bunch of children. We aren't the ones liable to impregnate a holy book with explosives. So ban the exploding Koran's, not the Chumashim.

The future of travel

My recent trip back from the UK (see the post below) had me musing on where this will all end up. We're now at the stage of no hand luggage and obligatory shoe checks. Perhaps the next plot will involve some other garment of clothing. So, on arrival at security, we'll be asked to take off all our clothes and wear a government supplied garment for the trip. When I mentioned this to my wife, she added that it had better be tnius (modest) or she wasn't going to fly. So then it hit me. The ultimate point of this Islamist plot. A chador for everyone!

Travelling light

As you are probably aware, terrorists in the UK have been plotting to blow up many US-bound airliners using liquid explosives. Consequently, security has been greatly tightened on all flights out of the UK, but especially those destined for the United States. All liquids, lotions, gels, creams etc. are now banned from cabin baggage. The only exception is baby food and formula, which you'll probably have to taste to prove they're edible. I saw a notice to this affect at the US airport I arrived at, so it appears to be a new universal rule.

For the US flights out of the UK, however, no hand baggage at all is allowed. The only exception here is one clear plastic bag with your travel documents, wallet, and keys, as well as the minimum quantity of prescription medicine (non-liquid) and hygiene items needed for the trip. That's it. No exceptions. You could buy non-liquids after passing through security and get them on the plane, provided you had the receipt. So, everyone in the waiting area was on page one of their book.

Now as someone travelling with N>>1 children, and used to shlepping several heavy bags containing: tallis & tefillin, laptop computer, cameras, food for the trip, entertainment for the children, changes of clothing for the little ones, this was a little daunting. But, like the restrictions imposed by keeping Torah, it was actually quite liberating and enlightening.

For one thing, there was little chance we'd forget anything on the plane. Disembarkation was faster since there was nothing for anyone else to pick up either. And it was great for working on your bitachon (trust in G-d). Would the airplane have kosher meals on board? Would your stuff survive the trip in the hold? Would the children drive you crazy? Or even sit in their seats without bribes?

For us it worked out just fine, but I can imagine any series of possible disasters, especially if we'd had to make a connecting flight. Still, I'll have to give some serious thought to how much to take on board next time.

Return from the mysterious east

The absence of postings over the past three weeks has not been due to a lack of material, but more a lack of easy internet access while travelling abroad. We've been visiting various places located between 52 and 53 degrees North latitude and 1 degree East and 5 degrees West longitude and I have several new observations to post. I'll try and dole these out over the next few days as I get back into a more routine schedule.